This invention relates to filling trenches in semiconductor manufacture.
It is known in the semiconductor wafer manufacturing art to create depressions or trenches and then fill them with a semiconductor material. However, for any one layer being worked on at a time, the manufacturer is confronted with an xe2x80x9call or nothingxe2x80x9d choice of using only one kind of fill material for all the open trenches on the semiconductor substrate. What is needed is a method to permit different fill materials to be used for different open trenches.
Described herein is a method of providing variant fills in a semiconductor substrate having a plurality of trenches wherein it is desired to fill a first set of the trenches with a first fill material and a second set of the trenches with a second fill material. The method begins by first filling all the trenches with the first fill material. The second set of trenches are then masked in a manner effective in resisting an etching operation on the first fill material. An etching operation is then effected which only etches the fill in the unmasked first set of trenches. This first fill material is not etched out completely, but only enough to leave room for a plug at the top of the trench. The first set of trenches is then plugged with a material resistant to an etching of the first fill material, so that now the first fill material in the plugged trenches is protected. Now, another etching operation is carried out (after the mask on the second set of trenches has been stripped off) so as to completely remove all of the first fill material from the second set of trenches. With the first set of trenches plugged, it is a straightforward matter to then fill in the newly emptied second set of trenches with a second fill material as desired.